848 



THE NERVOUS SYSTEM 



mid-line, to fuse with the like bundle from the hippocampal gyri of the opposite side. 

 The bundles thus arising from the two sides are the posterior pillars or crura of the 

 fornix. They appear as two flattened bands of white substance which come in close 

 contact with and even adhere to the splenium. 



The angle formed by the mutual approach of the posterior pillars of the fornix is 

 crossed by a lamina of commissural fibres connecting the hippocampal gyri of the 

 two hemispheres (fig. 631 ). This lamina is the hippocampal commissure (psalterium 

 or lyra), and being of a different functional direction, should not be considered a 



FIG. 629. DIAGRAM SHOWING FORNIX AND ITS CONNECTIONS AS SEEN FROM ABOVE. 

 OLFACTORY BULB 



MEDIAL OLFACTORY STRIA 

 SUBCALLOSAL GYRUS 

 ANTERIOR cmo/.v 



FIMBRIA 



THA LA MO-MA MMILLA R Y 



FASCICULI'* 

 STRIA TERM I. \~ALIS OP 



THALAMUS 

 STRIA MEDULLA RIS OF 



THA LAM US 

 POSTERIOR PILLAR 



EPIPHYSIS 



DIGITATIOXS (PES) OF THE 

 HIPPOCAMPUS 



AMYGDALOID NUCLEUS 



-- JIIPPOCAMPUS MAJOR 



y~ -5-v< ^ / 

 \3Kx 



IIUTOC.IMPAL COMMISSURE (LYRA) 



part of the fornix. Usually the hippocampal commissure and the posterior crura 

 are in close contact with the under surface of the splenium. When occasionally 

 they do not adhere, the space between is known as Verga's ventricle. 



The body of the fornix appears as a triangular plate of white substance produced 

 by the fusion of the pillars. Its base or widest portion is behind. It is not always 

 bilaterally symmetrical. Its upper surface is attached by the septum pellucidum to 

 the under surface of the corpus callosum. Below, it lies over the tela chorioidea of 

 the third ventricle, which separates it mesially from the cavity of the third ventricle 



FIG. 630. DIAGRAM OF COURSE OF FORNIX AS VIEWED FROM THE SIDE. 



ANTERIOR COLUMN 



OLFACTORY BULB 

 CORPUS MAMMILLA RE 



SUBCALLOSAL GYRUS 



POSTERIOR PILLAR 



STRIA TKRMIXALIS 

 OF THALA.1ir.-i 



HIPPOCAMPUS MAJOR 



FIMIIRIA Hi- IIIPPO- 



CAMPDS 



AMYGDALOID 

 NUCLEUS 



DIC.ITA TIO\S ( PES) OF 

 THE HIPPOCAMPI'S 



and laterally from the upper surfaces of the thalami. Its sharp lateral edge or mar- 

 gin (tsenia fornicis) projects into the lateral ventricle of either side in relation with 

 the chorioid plexus of that ventricle, and thus the lateral portion of its upper surface 

 forms part of the floor of the lateral ventricle an arrangement to be expected, since 

 the posterior pillars arise from the floor of the ventricle, viz., the hippocampus. The 

 ventricular portion is covered by a layer of ependyma in common with that lining the 

 rest of the ventricle. 



